With the increased costs of petroleum resources, the diminishing known reserves of petroleum, as well as the increased costs of exploring for new petroleum reserves, the petroleum production and refining industry has utilized enhanced recovery techniques to produce petroleum and gas from non-naturally producing reserves and from formerly naturally producing reserves which have been partially or substantially depleted. Enhanced recovery techniques include a wide range of manipulations to recover petroleum and gas from petroleum bearing geologic formations, including miscible gas pressurization, selective liquid flooding and in-situ combustion or fireflooding.
Commercial in-situ combustion projects involves the placement of one or more of injection wells in the vicinity of a single or plurality of production wells. Air, oxygen enriched air or potentially pure oxygen is introduced into the petroleum bearing formation through an injection well and either spontaneously combusts a portion of the petroleum reserve or supports combustion induced by other means. The in-situ oxygen-fed combustion typically moves in a wave front through the petroleum bearing formation from the injection well to the production well. Occasionally, the oxygen gas introduced into the injection well comprising air, oxygen enriched air or oxygen, breaks through the wave front or otherwise bypasses the wavefront and appears as uncombusted gas in the production well produced gas. Additionally, the combustion may form substantial quantities of carbon monoxide which are co-produced with the hydrocarbon gases normally produced in association with petroleum production. The presence of an oxygen-containing gas, carbon monoxide, hydrocarbon gases and vapors, as well as possible hydrogen and hydrogen sulfide in the production well presents a potential problem for flammability or detonation.
Techniques for flammability and detonation detection and control for in-situ combustion projects have not been practiced in the prior art. Operators of in-situ combustion petroleum recovery projects have either been unaware of the potential production well flammability and detonation hazard, have chosen to operate the project regardless of the hazardous condition or have merely shut the wells in and closed them down. Those in-situ combustion wells that have presented serious combustion problems, or in fact, have undergone combustion or detonation have merely been shut in and closed off by known methods, such that the well is no longer useful for the production of petroleum. The petroleum production industry has previously felt that work in petroleum fields with flammable or detonable produced gas mixtures is an assumed risk which has not warranted monitoring and control techniques.
The present invention overcomes the safety drawbacks of the prior art practice of in-situ combustion petroleum recovery as set forth below.